Flat panel detectors for use in x-ray radiation imaging systems are known. Examples of these pixel sensor arrays can be found in U.S. Pat. Nos. 5,184,018 and 5,381,014. One such type of flat panel detector includes a thick amorphous selenium film (a-Se) on a two-dimensional TFT switch array. The TFT switches are arranged in rows and columns to form a two-dimensional imaging system. Gate lines interconnect the TFT switches in each row while source lines interconnect the TFT switches in each column. The thick selenium film is deposited directly on top of the TFT switch array and a top electrode is deposited on the selenium film.
When x-rays are incident on the selenium film and the top electrode is biased with a high voltage, electron-hole pairs are separated by the electric field across the thickness of the selenium film. The holes which are driven by the electric field move toward the pixel electrodes (i.e. the drain electrodes of the TFT switches) and accumulate. This results in a charge being held by the pixel electrodes which can be used to develop an x-ray image. The charge held by the pixel electrodes can be read by supplying a pulse to each gate line. When a gate line receives a pulse, the TFT switches in the row turn on, allowing the signal charges on the pixel electrodes to discharge through the TFT switches on to the source lines. Charge amplifiers connected to the source lines sense the charge and provide output voltage signals proportional to the charge and hence, proportional to the radiation exposure on the selenium film.
Although this pixel design is satisfactory, alternative designs are continually being sought. It is therefore an object of the present invention to provide a novel flat panel detector for radiation imaging and a pixel for use therein.